1. Field of the Invention
The present invention relates to a black coating film and a production method therefore, a black light shading plate, and a diaphragm, a diaphragm device for light intensity adjustment, a shutter using the same, and a heat resistant light shading tape, and in more detail, the present invention relates to a heat resistant black coating film which is capable of making the surface of optical members to be low reflection property and black property, a black light shading plate having a resin film etc. using the same as a base substrate, and a diaphragm, a diaphragm device for light intensity adjustment, a shutter using the same, and a heat resistant light shading tape.
2. Description of the Prior Art
In recent years, development of a high-speed (mechanical-type) shutter of a digital camera has been performed actively. It is because increase in shutter speed enables to provide photographing of an ultra high-speed photographic subject without blurring and thus provide a vivid image. In general, a shutter is opened and closed by rotation and moving of a plurality of blades called shutter blades, and in order to increase shutter speed, weight reduction and high sliding property are required so that the shutter blades operate and stop in an extremely short period of time. Still more, the shutter blades have a role to shade light by covering the front surface of a photo-sensitive material such as a film, or an image sensor such as CCD or CMOS, and are required to have complete light shading property. Not limiting thereto, the shutter blades are desired to have low light reflectance, that is, high black degree, at the blade surface, to prevent generation of leaked light among each of the blades, in actuation of a plurality of shutter blade pieces in an overlapping way each other.
As for a fixed diaphragm to be inserted in a lens unit of a digital camera, which has a role to transmit light to the image sensor after squeezing to a certain quantity of light, it is also desired to have low light reflection property, that is, high black property, at the surface, because generation of light reflection at the diaphragm surface makes stray light and impairs vivid imaging.
In recent years, also in a mobile phone having photographing function, that is, a camera-equipped mobile phone, a compact mechanical-type shutter has started to be mounted in the lens unit, so as to enable to take a photo with high pixel and in high quality. In addition, inside the lens unit of a mobile phone, a fixed diaphragm is inserted. The mechanical-type shutter to be incorporated in the above mobile phone requires the operation under more saved power as compared with a general digital camera. Therefore, weight reduction of the shutter blades is particularly strongly required. Still more, in recent years, in production of the lens unit of a mobile phone, aiming at reduction of production cost, it is desired that each of the parts such as a lens, a fixed diaphragm and a shutter can be assembled in the reflow step. Therefore, heat resistance in addition to low light reflection property and black property at the surface are required for the shutter blades or the fixed diaphragm to be used therein.
In addition, in viewing a recent trend of an apparatus mounted on an automobile, there is a trend that a monitor using a video camera such as a back-view monitor is mounted. A fixed diaphragm is used also in the lens unit of this video camera monitor, and low reflection property, and black property are required for the diaphragm surface, similarly to prevent stray light. And heat resistance is required for the lens unit of the automotive video camera, so that function is not impaired even under high temperature use environment such asunder scorching sun in midsummer, and heat resistance is required also for the fixed diaphragm member.
On the other hand, a liquid crystal projector has recently started prevailing at ordinary households, because it makes viewing possible as a home theater with a large screen. Enhancement of picture quality has been desired strongly so that a vivid and high-contract projected image can be enjoyed, even under bright environment such as in a living room, and higher brightness of picture quality by increased output of a lamp light source is progressing. A diaphragm device for light intensity adjustment (auto iris) to adjust light quantity from the lamp light source is used at the inside or the side surface of the lens system, in an optical system of a projector. In the diaphragm device for light intensity adjustment, area of an opening part, which transmits light, is adjusted by overlapping of a plurality of diaphragm blade pieces each other, similarly as in a shutter. Low reflection property at the surface and weight reduction thereof are also required for the diaphragm blades of such a diaphragm device for light intensity adjustment, because of the similar reason as in the case of the shutter blades. At the same time, because the diaphragm blades of the diaphragm device for light intensity adjustment are heated by irradiation of the lamp light, heat resistance is also necessary. That is, it is because degeneration and deterioration of low reflection property of a blade material caused by light irradiation generate stray light, and cannot take a vivid projected image.
The following materials are used generally in response to required characteristics, for a light shading plate to be used for the above shutter blades, the fixed diaphragm material and the diaphragm blades of the diaphragm device for light intensity adjustment.
In the case where heat resistance is required, generally, a light shading plate made of a thin plate of a metal such as SUS, an SK material, Al, or Ti is used as a substrate. There is the case where the thin metal plate itself is used as the light shading plate, however, because of having metallic gloss, it is not preferable in the case where influence of stray light caused by reflected light at the surface should be avoided. On the other hand, a light shading plate having black and lubricating coat on the metal thin plate has a problem of inability of general use under high temperature environment, because of having inferior heat resistance at the coated part, although having low reflection property and black property. In Patent Document 3, there has been disclosed a light shading material, where a hard type carbon film is formed at the surface of a blade material made of a metal such as an aluminum alloy. However, low reflection characteristics of the light shading material cannot be attained even by formation of the hard type carbon film onto the surface, and generation of stray light caused by reflected light is unavoidable. In the case of the light shading plate where the above metal thin film is used as a substrate, use thereof as the shutter blades or the diaphragm blades raises a problem of increased torque of a drive motor for driving the blades, increased power consumption, inability to increase shutter-speed and generation of noise caused by contact of blades themselves, because of heavy weight in any cases.
On the other hand, a light shading plate using a resin film as a substrate has also been proposed. In Patent Document 1, there has been proposed a light shading plate using a resin film, which is matte-processed to reduce reflection at the surface, or a film-like light shading plate furnished with matte property by forming a surface with multiple fine irregularities, and also in Patent Document 2, there has been proposed a light shading film, wherein a thermosetting resin containing a matte paint is coated on a resin film. However, they only reduce reflection at the surface by processing the resin film itself, or by the addition of a matte agent, and there is no consideration on prevention of influence of stray light cause by reflection from the light shading blades.
As for the light shading plate using a resin film as a substrate, polyethylene terephthalate (PET) is used as a substrate in many cases, because of low specific gravity, low price and flexibility. In addition, such a PET film is widely used that has reduced transmittance by impregnation of black fine particles such as carbon black or titanium black to inside. For example, in Patent Document 4, there has been proposed coating a substrate with a coating film containing a needle-like or particulate micro material of titanium oxide or the like.
However, the PET material has a heat resistance of lower than 150° C., and weak mechanical strength such as tensile modulus of elasticity. Because of inferior heat resistance, it cannot be utilized as a diaphragm member for light intensity adjustment of a projector which is irradiated by high output lamp light, or a fixed diaphragm member or a shutter member which enables to correspond to the reflow step. In addition, in the blade member of a high-speed shutter, it is required to reduce film thickness in response to higher-speed of the shutter blades, and in the case of the resin film obtained by impregnation of black fine particles inside, it is impossible to exert sufficient light shading property, when film thickness decreased to, for example, 38 μm or thinner, and thus it cannot be used as the shutter blades.
In Patent Document 5, there has been proposed a light shading blade material obtained by sequentially laminating a thin film composed of a metal simple substance, a mixture or a compound, which is obtained by film-formation by a sputtering method or the like on a resin film, and a thin film (a protective film) composed of a simple substance or a mixture or a compound of a specific element, which satisfies characteristics of electrical conductivity, lubrication property and scratch resistance. Here, there is no description of low reflection property and black property, which are characteristics required for recent light shading blades. In addition, there is no specific description of effect of the protective film, other than effect of carbon on scratch resistance.
As described above, although there are coating film materials for making the surface of optical parts such as the shutter blades or the fixed diaphragm, or the diaphragm blades of, the diaphragm device for light intensity adjustment, low reflectance and black color, those excellent in heat resistance have not been found.
Under these circumstances, there has been required the light shading plate using a thin film of a metal, having relatively light weight, such as SUS, SK material, Al or Ti, or a resin film furnished with low reflection property and black property, as a substrate, which does not increase torque or power consumption of a drive motor for driving the blades, and enables to increase shutter speed, and does not generate noise caused by contact of the blades themselves, and shutter blades or the fixed diaphragm, and the diaphragm blades for the diaphragm device for light intensity adjustment, having all of sufficient light shading property in a visible light region and low reflection property, lightweight and electrical conductivity.
As described above, with progress of a more compact and thinner type of a digital camera and a camera-equipped mobile phone, more compact and thinner types of component parts to be mounted have been required as well, and there is a trend of a thinner type of an image sensor such as CCD or CMOS, or a flexible printed circuit substrate (FPC) mounted with an image sensor. In this case, light leaks from the rear surface of the image sensor, and still more, light passes through also the FPC. This transmitted light reflects at the parts of the FPC side and passes again through the FPC and enters from the rear surface of the image sensor. Increase in leaked light to this rear surface of the image sensor causes viewing of an image of a wiring circuit of the FPC into an imaging region, resulting in deterioration of quality of the imaging. Therefore, it is considered effective that a lightweight light shading film, having function to absorb and shade light, adheres onto the FPC, so that light, which transmitted from the rear surface of the image sensor, should not return again. In the case where a camera unit enables to correspond to reflow, heat resistance is also required for the light shading film.
There is no heat resistant light shading tape effective to such applications up to now, and development thereof has been required.    [Patent Document 1] JP-A-1-120503    [Patent Document 2] JP-A-4-9802    [Patent Document 3] JP-A-2-116837    [Patent Document 4] JP-A-2002-40512    [Patent Document 5] JP-A-2006-138974